AUTOMATIC TRANSFER SWITCHES

1
John Stark Russelectric Inc.
2
Overview
Recent changes to the National Electrical Code
(NEC) require the selective coordination of
overcurrent protective devices at hospitals and
other mission-critical facilities.
Transfer switches with 30-cycle closing and
withstand ratings dramatically simplify designing
to that requirement.
3
Transfer Equipment in a Common Scenario
With regard to the emergency back-up and transfer
scheme, it is incumbent upon engineers to select
the proper equipment for the application. There
are many considerations and they are becoming
more with each decade.
4
What is Selective Coordination?

• Definition (Article 100 NEC)
• Localization of an overcurrent condition to
  restrict outages to the circuit or equipment
  affected, accomplished by the choice of
  overcurrent protective devices and their ratings.

Article 100 provides the Code definition. Here is
another way to describe it
For the full range of possible overcurrents, the
act of isolating an overloaded or faulted circuit
from the remainder of the electrical system,
thereby eliminating unnecessary power outages.
The circuit causing the overcurrent is isolated
by the selective operation of only that
overcurrent protective device which is closest
upstream to the overcurrent condition.
5
Selective Coordination, History Requirements
Selective coordination was first required by the
NEC in 1993 for elevator circuits. Amendments to
the Code in 2005 and 2008 strengthened the
requirements and expanded them to include
emergency and legally required standby systems,
as well as critical operations power systems.
Selective coordination, as defined in the 2008
NEC, is the (as in previous slide) localization
of an overcurrent condition to restrict outages
to the circuit or equipment affected,
accomplished by the choice of overcurrent
protective devices and their ratings or
settings. It is a complicated process of
coordinating the ratings and settings of
overcurrent protective devices, such as circuit
breakers, fuses, and ground fault protection
relays, to limit overcurrent interruption (and
the resultant power outages) to the affected
circuit or equipment (the smallest possible
section of a circuit). In other words, the only
overcurrent protective device that should open is
the device immediately upstream from the
circuit/equipment experiencing an overcurrent
condition.
6
Proper Selective Coordination is becoming more
and more of an engineering consideration and is
being enforced by inspectors more more often
Refer to IAEI handout Selective coordination
restricts outages to the circuit or equipment
affected, ensuring reliability of electrical
power.
7
NEC 2008 Verbiage on Selective Coordination

• NEC(2008) 700.27 Coordination requires
  Emergency system(s) overcurrent devices shall be
  selectively coordinated with all supply side
  overcurrent protective devices.
• NEC(2008) 701.18 Coordination requires Legally
  required standby system(s) overcurrent devices
  shall be selectively coordinated with all supply
  side overcurrent protective devices.
• NEC(2008) 517.26 Application of other articles
  requires The essential electrical system shall
  meet the requirements of Article 700.
• The overcurrent protective devices may
  include the following
• Molded Case Circuit Breakers
• Fused devices
• Insulated Case Circuit Breakers
• Air Power Circuit breakers

8
More on Selective Coordination
9
One-line
Utility
4000A APCB
1600A APCB
1600A APCB
800A ICCB
400A MCCB
An overcurrent event (overload, short circuit,
or ground fault) here should trip the 400A MCCB
10
(No Transcript)
11
Selective Coordination
12
Review of Code Requirements

• Article 517 Health Care Facilities
• 517.26 Application of Other Articles
• Article 620 Elevators, etc
• 620.62 Selective Coordination (2008)
• Article 700 Emergency Systems
• 700.9 (B)(5)(b), Exception
• Article 701 Legally Required Standby Systems
• 701.18 Coordination
• Article 708 Critical Operations Power Systems
• 708.54 Selective Coordination

13
2005 Code Adoption
14
2008 Code Adoption
WA
ME
ND
MT
VT
M I
MN
NH
MA
OR
NY
WI
CT
SD
ID
RI
M I
WY
NJ
PA
IA
NB
OH
DE
MD
Expected July 2010
IN
NV
WV
IL
Expected July 10
UT
VA
CO
MO
KS
KY
CA
NC
Expected January 2011
TN
State Adopted
SC
AR
AZ
NM
OK
S. Carolina Code Council adopted 2009 IRC with
2008 NEC 3/22/10 with implementation
effective 1-1-11
TX
GA
AL
MS
LA
State Adopted Unincorporated Areas
AK
FL
AK
HI
2008 NEC 32 States
HI, basically 2002 NEC but some islands back to
1993 NEC
2005 NEC 8 States
Local Adoption (10)
Note Some local adoption states have earlier
than 2005 adoptions in some jurisdictions
Revised April 19, 2010
15
Code Rulings
In the 2008 Code Cycle there were challenges to
the selective coordination requirement. Proposal
13-135 proposed the elimination of the selective
coordination requirement for 700.27. The
proposal was to remove the selective coordination
requirement from the mandatory text and places it
in a non-mandatory in a FPN (fine print note).
But Code Panel 13 rejected this proposal by a
vote of 9-4. To follow is their statement

• Panel 13 Statement
• This proposal removes the selective coordination
  requirement from the mandatory text and places
  it in a non-mandatory FPN (fine print note). The
  requirement for selective coordination for
  emergency system over-current devices should
  remain in the mandatory text. Selective
  coordination increases the reliability of the
  emergency system. The current working of the NEC
  is adequate. The instantaneous portion of the
  time-current curve is no less important than the
  long time portion. Selective coordination is
  achievable with the equipment available now.

Then, Code Panel 20, which was responsible for
the new Article 708, summed up the need for
selective coordination in their statement to
Comment 20-13, (which was another proposal for
the deletion of the selective coordination
requirement).
This comment was rejected 16-0. The actual panel
statement to Comment 20-13

• Panel 20 Statement
• The overriding theme of Articles 585 (renumbered
  to 708) is to keep the power on for vital loads.
  Selective coordination is obviously essential for
  the continuity of service required in critical
  operations power systems. Selective coordination
  increases the reliability of the system.

16
Exceptions to Code RulingsRefer to IEEE handout
Selective Coordination versus Arc Flash page 12
There are numerous proposals being adopted by
States and/or City or local governmental bodies
which modify the selective coordination
requirements.
The most commonly heard proposals fall into two
categories
1. Allow the degree of selective coordination
needed to be the responsibility of the qualified
person responsible for the project.
(The Commonwealth of Massachusetts was the first
State to adopt such a proposal as an exception to
the Articles in 700.27, 701.18 and 708.54, which
require selective coordination as follows
Exception No. 2 Where the system design is under
the control of a licensed professional engineer
engaged in the design or maintenance of
electrical installations, the selection of
overcurrent protective devices shall be permitted
to coordinate to the extent practicable. The
design shall be documented, stamped by the
professional engineer, and made available for
review by the authority having jurisdiction.
17
Exceptions to Code Rulings (cont.)
2. Proposals to modify the NEC requirement for
selective to only be required for above a
specific time. The leading proposal is 0.1
seconds (6 cycles) and above. The State of
Oregon recently adopted a proposal submitted by
the National Electrical Contractors Assoc.,
Oregon Pacific Cascade Chapter, as Statewide
Alternate Method No. OESC 08-04 applying to
Articles in 700.27, 701.18 and 708.54. This
states the following The requirements in NEC
700.27, 701.18 and 708.54 for selective
coordination may be demonstrated by providing a
selective coordination study utilizing trip-curve
data in the range of 0.1 seconds or more.
Substantiation for this proposal included
1). selective coordination is not always
possible or practical for all fault current
levels when protection is provided by MCCBs. The
requirement for total selective coordination
means that over current protection devices must
be coordinated for all faults, regardless of
their magnitude or duration, including the most
extreme case, the bolted fault. However, bolted
three phase faults which rapidly generate
extremely high current in the instantaneous range
rarely occur in practice, except at start-up when
interruption of power due to a lack of
coordination is not likely to compromise
safety... In order to achieve total short
circuit selective coordination, the size of
upstream overcurrent protective devices may need
to be increased and/or time delay trip
characteristics increased, thereby possibly
increasing the arc flash hazard.
Findings By omitting the instantaneous range
from the requirements for selective coordination,
reasonable and affective safety can (still) be
achieved. Signing supervisors and engineers can
use readily available and published time current
curves to determine if a system is selectively
coordinated to a substantial degree without
having to relay on unregulated manufacturer
testing data and inconsistent engineering and
design practices.
18
Arc Flash ConsiderationsRefer to IEEE handout
Selective Coordination versus Arc Flash page 10
This is the other side of the argument regarding
the subject of Selective Coordination VS Arc
Flash Considerations.
The presenter will not delve into this side of
the argument, as he is in the business of
providing emergency power to critical facilities
and therefore is in the camp of having a
non-sensitive, robust type system, selectively
coordinated, that facility managers want to
perform well when called upon. In cases of
catastrophic outages, Arc flash considerations
might take a back seat to keeping as much of the
facility up and running as possible and only
Tripping CBs closest to the fault. For more
details on the ARC Flash concerns, and that whole
side of the argument, please refer to your
handout.
19
UL 1008 Withstand Test

• 34.1 When tested under the conditions described
  in 34.2 34.15, a transfer switch shall
  withstand the designated levels of current until
  the over-current protective devices open or for a
  time as designated in 34.3. At the conclusion of
  the test
• The switch shall be capable of being operated by
  its intended means
• The fuse mentioned in 34.14 shall not open,
• There shall be no breakage of the switch base to
  the extent that the integrity of the mounting of
  live parts is impaired,
• The door shall be prevented by its latch, without
  bolt or lock installed therein, from being blown
  open, and deformation of the door alone is not
  determined to be unacceptable
• No conductor shall have pulled out of a terminal
  connector and there is no damage to the conductor
  insulation or the conductor (see 41.56) and
• For a plug in or draw out unit, the point of
  contact is to be the same both mechanically and
  electrically as before the test.

20
UL 1008 Closing Test

• 36.1 When tested in accordance with 36.2, a
  transfer switch shall comply with the
  requirements in 34.1(a) (f).
• 36.1 Revised September 18, 1996
• 36.2 The sample for this test is to be that used
  for the withstand test. Test procedures and
  conditions for the closing test are to be as
  described in 34.3 34.19. The switch is to be
  closed on the circuit.
• 36.3. The test (for close on) current shall be
  the same as that used in the withstand
• test.

21
UL 1008 Short Circuit Test History

• Around 1989 UL introduced an optional 3
  cycle test for any over-
• current protection device.
• Prior to this, manufactures could test with any
  over-current device.
• If a manufacturer didnt test to 3 cycles, they
  would be required provide a label that lists all
  breakers that the switch was coordinated with.
• This requirement did not take into consideration
  air power circuit breakers APCBs. Some of these
  breakers were 4-5 cycle devices (GE AKR and
  Westinghouse DS)
• January 9th, 2002 UL introduced an optional
  short time current
• rating test.
• A withstand and a close and withstand test is
  required to get a UL short time rating.

• This requirement did not take into consideration
  air power circuit breakers APCBs. Some of these
  breakers were 4-5 cycle devices (GE AKR and
  Westinghouse DS)

22
UL 1008 Short Time Current Test

• 36A.1 A switch marked with a short-time current
  rating in accordance with 41.20.1 shall be tested
  under the conditions described in 36A.2 -36A.12
  and shall withstand the short-time current for
  the period specified. At the conclusion of the
  test
• The transfer switch shall be capable of being
  operated by its intended means,
• The fuse mentioned in 36A.7 shall not open,
• There shall not be any damage to the switch base
  to the extent that the integrity of the mounting
  of live parts is impaired,
• The door shall be restricted by its latch,
  without bolt or lock installed therein, from
  being blown open. Deformation of the door itself
  is not reason for rejection,
• No conductor shall have pulled out of a terminal
  connector and there shall not be any damage to
  the conductor insulation or the conductor (see
  41.56),
• For a plug-in or draw-out unit, the point of
  contact shall be the same both mechanically and
  electrically as before the test,
• The Temperature Test, Section 29, shall be
  performed on the transfer switch at the
  completion of the tests described in 36A.8 and
  36A.9, without maintenance, and the temperature
  rise shall not exceed the values given in Table
  29.1, increased by 10 C or 18 F, and
• The Dielectric Voltage-Withstand Test (Repeated),
  Section 36B, shall be performed on the transfer
  switch at the completion of the tests described
  in 36A.8 and 36A.9.

23
UL 1008 Overload Test

• 28.1 Transfer switch equipment shall perform in
  an acceptable manner, as intended by the
  manufacturer, when subjected to an overload test
  consisting of the number of operations specified
  in Table 28.1, controlling a test current as
  described in Table 28.2.
• Table 28.1 Overload Test

Table 28.2 Method of determining test current
for overload tests on transfer switches

28.4 A cycle is defined as making and breaking
the required test current on both the normal and
alternate contacts. During the test, the
alternate source shall be displaced 120
electrical degrees from the normal source for a 3
phase supply or 180 electrical degrees for a
single phase supply. 28.6 The minimum on time in
each contact position is to be 1/6 second (ten
electrical cycles based on a 60Hz source), unless
automatic tripping of the over-current device
occurs.
24
UL 1008 Endurance Test

• 30.1 A transfer switch shall perform as intended
  when subjected to an endurance test controlling a
  test current as described in Table 30.1 and at a
  rate and number of cycles described in Tables
  30.2 and 30.3.
• Table 30.1
• Method of determining test current for endurance
  tests
• The test cycle is to be 1 second on and
  59 seconds off. A controller may be operated at
  a rate of more than 1 cycle per minute if
  synthetic loads are used or if a sufficient
  number of banks of lamps controlled by a each
  bank will cool for at least 59 seconds between
  successive applications of current.
• Table 30.2
• Endurance test cycles for emergency system
  switches including legally required stand-by
  systems.

25
UL 1008 Temperature Test
29.1 Transfer switches when tested under the
conditions described in 29.2 29.12 shall not
attain a temperature at any point high enough to
constitute a risk of fire or to damage any
materials employed in the device, and shall not
show temperature rises at specific points greater
than those indicated in Table 29.1 29.2 For the
temperature test the transfer switch is to be
operated under intended use conditions and is to
carry its test current continuously at the test
potential specified in Table 24.1. 29.3 The test
current shall be 100 percent of the rated current.

26
Overcurrent Protective Devices

• Molded Case Circuit Breakers MCCB (UL489)
• May be Current Limiting to 200KA
• Long Time Overcurrent
• Instantaneous Interruption is less than 3 cycles
• Fuses and Fused Devices
• Current Limiting
• Mostly used on 200KA circuits
• Insulated Case Circuit Breakers -ICCB (UL489)
• May be Current Limiting to 200KA
• Instantaneous Interruption is typically less
  than 4 cycles
• Short Time delay available (30 cycles) with
  Instantaneous over-ride
• Low Voltage Air Power Circuit Breakers -APCB
  (UL1066)
• May be Current Limiting to 200KA
• Instantaneous Interruption is typically less
  than 4 cycles
• Short Time delay available (30 cycles) without
  Instantaneous

27
Low Voltage Air Power Circuit Breakers

• APCBs are ideal protective devices for the
  application of selective tripping.
• Short Circuit Duty Cycle Oc,15 s CO
  (applying fault current
• to a closed CB for ½ second 30 cycles
  separated by 15 seconds
• of zero current flow, then close on fault
  current for another ½
• second 30 cycles ).
• This test may be performed with or without an
  instantaneous override on the closing cycle.
• The GE AKR was tested without the instantaneous.
  Note some breakers now have a Trip Free feature
  in which the breaker will still clear a fault
  without instantaneous trip. Opinions vary on
  whether this is desirable or not in emergency
  power systems.
• Short Time Current
• ANSI C37.13.10.2.1(2)-1990
• Short-Time Current Duty Cycle Application. The
  applicable short-time current duty cycle for
  unfused circuit breakers consists of two periods
  of 1/2s current flow, separated by a 15 s
  interval of zero current.

28
Selective Coordination - Good
No overlapping fault current of individual
devices. This is coordinated properly. In a
perfect world this is great.
29
Selective Coordination - BAD
In this case, since it takes 8 cycles for the
upstream breaker to clear the fault, a 3 cycle
rated transfer switch is inadequate.
30
Complete Coordination
A 30 cycle UL rated Transfer Switch truly gives
you complete coordination with any over-current
protective device.
31
New Russelectric 30 Cycle Automatic Transfer
Switchesand Bypass Isolation Switches
32
Back Plate Assembly
BACKPLATE -increased thickness to 1.25 -added
strength and stability

• SIDE BARRIER
• 5/8 thk glass polyester
• Greater arc track resistance
• Excellent flame resistance
• Movable contact support

33
CROSSARM MECHANISM

• Made from 1.125 Square Steel Stock
• Overcenter Spring Mechanism to Latch Contacts
  Closed and Open
• Utilizes same mechanics as the 3 cycle
  switch Heavier spring

34
OPERATORS

• Open Transition Switches with EMO
• Reliability of Motor Operators

35
30 CYCLE BYPASS SWITCHES

• Major Design Changes
• Elimination of Isolation Handle
• Gearbox, Rack-in Mechanism to engage switch
• Bottom and Side Guiderails to align and Contain
  Switch
• Secondary Disconnects accessible on Left side of
  cabinet
• Optional Shutter Design
• 800A Cradle is On the Ground Rollout Design
• Complete Finger Cluster Redesign for all Sizes
• ATS Contacts Redesign

36

• Removal of Isolation Handle

• Single Handle is for Bypass Operation

• 800A Rollout Switch

Cradle rolls out on Ground not on rails
37
Gearbox Rack-in Mechanism

• Access Rack-in Shaft through door - only in
  Bypass Mode

• Position Indicator Window
• - Connected
• - Connected Bypassed
• - Test
• - Isolated

• Gearbox needed for Increased Spring Pressure
• - Must Pass the Liz Test

38
Secondary Disconnect

• Located on left Side of Cubicle for accessibility

• Allows for Test Position

• Incorporated into Side Guide-Rail

39
Guide Plates

• Used for Left to Right Alignment

• Prevents Rollout Switch from jumping or
  shifting during fault

40
Shutter Design (Optional)
Shutter Closed (switch in test position or
isolated)
Shutter Open (switch racked-in)
41
Finger Clusters

• Added Spring Pressure for Clamping

• Increased Contact Surface Area

• Withstood 100KA for 3 Cycles and 85KA for 30
  Cycles - without a scratch

2500A Cluster
800A Cluster